Chemical Bonding and Life

Hydrogen bonds are responsible for most of water's unique properties, such as its high boiling point, ability to dissolve many substances, and surface tension.

Water's high specific heat allows it to absorb and release heat energy slowly, moderating temperature changes and creating stable environments. This helps stabilize coastal climates and drives ocean currents.

Carbon's ability to form four stable covalent bonds with other atoms, including itself, allows it to create a wide variety of complex molecules essential for life, such as carbohydrates, lipids, proteins, and nucleic acids.

Functional groups are specific groups of atoms within molecules that impact their properties, reactivity, and interactions with other molecules.

Amino acids contain two main functional groups: the amino group (-NH₂) and the carboxyl group (-COOH). The amino group acts as a base, accepting protons (H⁺), while the carboxyl group acts as an acid, donating protons (H⁺).

ATP, adenosine triphosphate, is the primary energy carrier in living systems. It stores and releases energy by breaking its high-energy phosphate bonds, powering cellular processes such as metabolism, muscle contraction, and DNA synthesis.

Dehydration (condensation) reactions remove water to form a bond, while hydrolysis reactions break bonds by adding water.

Humans possess the enzyme amylase, which breaks down the α-glucose bonds in starch. However, humans lack the enzyme to break down the β-glucose bonds in cellulose, making it indigestible.

Hershey and Chase used bacteriophages labeled with radioactive sulfur and phosphorus to demonstrate that DNA, not proteins, is the genetic material.

Griffith's experiment with Streptococcus pneumoniae bacteria showed that harmless bacteria could become virulent by acquiring genetic material from heat-killed virulent bacteria, demonstrating transformation.

Meselson and Stahl used isotopic labeling to prove that DNA replication is semiconservative, meaning each new DNA molecule retains one original strand with an added new strand.

In DNA, Adenine (A) pairs with Thymine (T) and Guanine (G) pairs with Cytosine (C), meaning the proportions of each base pair are equal due to base pairing. This was discovered by Chargaff.

During DNA polymerization, nucleotides are added to the 3' end of the growing DNA strand. This is due to the 3' OH group on the sugar, which provides the site for the next nucleotide's phosphate group.

DNA strands run in opposite directions, with one strand going from 5' to 3' and the other from 3' to 5'. This arrangement is crucial for accurate base pairing and enzyme function.

The leading strand is synthesized continuously because DNA polymerase moves in the same direction as the replication fork. The lagging strand is synthesized discontinuously in short segments called Okazaki fragments due to the opposite movement of DNA polymerase from the fork.

An enzyme that adds nucleotides to a growing DNA strand during replication, proofreads for errors, ensuring accurate replication of genetic information.

Topoisomerase relieves the strain caused by the unwinding of the DNA helix during replication by temporarily breaking and rejoining the DNA strands, preventing overtwisting.

A viral replication cycle where the virus infects a host cell, replicates using the cell's machinery, assembles new viral particles, and finally bursts the cell to release the new viruses.

Metabolic pathways that build complex molecules from simpler ones, requiring energy input. Think of building blocks.

Metabolic pathways that break down complex molecules into simpler ones, releasing energy. Think of dismantling.

Biological catalysts that speed up chemical reactions by lowering the activation energy required. Think of a matchmaker.

A regulatory mechanism in which the end product of a metabolic pathway inhibits an enzyme that acts earlier in the pathway. Think of a self-regulating system.

The process where glucose is oxidized, releasing energy in the form of ATP, while oxygen is reduced, forming water. Think of a battery.

Glucose is broken down into two pyruvate molecules, generating a small amount of ATP and reducing NAD+ to NADH. Think of the first step of a long journey.

The citric acid cycle produces NADH, FADH2, and ATP, as well as carbon dioxide waste. Think of a central hub of energy production.

A series of protein complexes embedded in the mitochondrial membrane that utilize electrons from NADH and FADH2 to pump protons (H+) across the membrane. Think of a waterfall powering a turbine.

The process where cells produce ATP from glucose without oxygen. Think of a backup battery.

Photosynthesis converts light energy into chemical energy (glucose), while cellular respiration breaks down glucose to produce energy (ATP) for cells. Think of a cycle of energy conversion.

The light reactions produce ATP, NADPH, and oxygen. Think of the energy gathering stage of photosynthesis.

Oxygen is produced during the light reactions when water molecules are split, providing electrons for the electron transport chain. Think of a side product of energy production.

Electrons are excited by light energy in photosystem II, passed through an electron transport chain, and re-excited in photosystem I before being used to reduce NADP+ to NADPH. Think of a relay race.

A target cell must have specific receptors for the signaling molecule. Think of a lock and key.

Kinases are enzymes that add a phosphate group to a target molecule. Think of an on-off switch.

Membrane proteins that open or close when a specific signaling molecule binds to them, allowing ions to flow in or out of the cell, thus changing the cell's membrane potential.

Small molecules that relay intracellular signals in response to external signaling molecules. They amplify the signal and trigger cellular responses.

A series of phosphorylation events within a cell that amplify a signal and trigger a response.

Cells only respond to signals that match specific receptors on their surface or inside the cell.

Hormones with opposing effects that maintain homeostasis. For example, insulin lowers blood glucose levels while glucagon raises them.

Helper T cells become activated when they encounter an antigen-presenting cell (APC) displaying a foreign antigen on its MHC class II molecule.

B cells produce antibodies that bind to pathogens and neutralize them, while cytotoxic T cells directly kill infected cells by recognizing foreign antigens on MHC class I molecules.

The immune system has a memory of past infections, allowing for a faster and stronger immune response upon re-exposure.

Helper T cells interact with both B cells and cytotoxic T cells to help activate them.

G1: The cell grows and prepares for DNA replication. S: DNA is replicated. G2: The cell continues to grow and prepares for mitosis.

Prophase: Chromosomes condense, the nuclear envelope dissolves, and spindle fibers form. Metaphase: Chromosomes align at the equator. Anaphase: Sister chromatids separate and move to poles. Telophase: Nuclear envelopes reform. Cytokinesis: Cytoplasm divides.

DNA amount doubles during the S phase and remains doubled throughout the G2 phase and mitosis, where it is equally divided between the two daughter cells.

Chromosomes are long DNA strands carrying genetic information, while sister chromatids are identical copies of a chromosome formed during replication, connected by a centromere and separated during mitosis.

Cyclins are proteins that bind to and activate cyclin-dependent kinases (CDKs), which are enzymes that phosphorylate target proteins to regulate the cell cycle.

Microtubule structure that organizes and separates chromosomes during mitosis.

Saturated fats are solid at room temperature, have no double bonds between their carbon atoms, and are fully saturated with hydrogen atoms. Unsaturated fats are liquid at room temperature due to the presence of one or more double bonds between their carbon atoms. These double bonds create 'kinks' in the molecule, preventing tight packing.

Saturated fats make cell membranes stiffer and less fluid, reducing flexibility and protein movement. Unsaturated fats, with their 'kinks,' increase membrane fluidity, allowing for greater flexibility and easier protein movement. This fluidity is crucial for many cellular processes.

The 20 unique amino acids are distinguished by their side chains (R-groups), which vary in size, charge, polarity, and chemical properties. These variations determine the amino acid's function in proteins and influence the protein's overall structure and behavior.

The 5' end of a nucleic acid has a phosphate group attached to the 5' carbon of its sugar molecule. The 3' end has a hydroxyl group (-OH) attached to the 3' carbon of its sugar. This directionality is essential for many crucial processes like DNA replication and transcription.

Prokaryotic cells are simpler, smaller, lack a nucleus and membrane-bound organelles. Their DNA is housed in a single circular chromosome. Eukaryotic cells are more complex, larger, have a nucleus containing their DNA, and possess membrane-bound organelles like mitochondria and the endoplasmic reticulum.

Plant and animal cells share several structures crucial for basic cellular functions. These include the nucleus, cytoplasm, cell membrane, mitochondria, and ribosomes. These structures are essential for energy production, protein synthesis, and genetic material storage, among other functions.

The maximum size of a cell is limited by the surface area-to-volume ratio. As a cell grows, its volume increases faster than its surface area, making it challenging to efficiently transport nutrients and waste across the membrane. This limitation prevents cells from becoming too large.

The nucleus stores DNA and controls cell activities. Mitochondria produce ATP through cellular respiration, providing energy. The rough ER synthesizes proteins, while the smooth ER handles lipid synthesis and detoxifies substances. The Golgi apparatus modifies, sorts, and packages proteins and lipids. Ribosomes synthesize proteins. Lysosomes break down waste. The plasma membrane controls substance entry and exit and maintains homeostasis.

Proteins destined for secretion are first synthesized on ribosomes attached to the rough ER. After synthesis, they are folded and modified in the ER before moving to the Golgi apparatus. In the Golgi, they undergo further modifications and are packaged into vesicles, which then fuse with the plasma membrane, releasing the protein outside the cell through exocytosis.

Small, nonpolar molecules like oxygen (O₂), carbon dioxide (CO₂), and lipids can easily diffuse through the plasma membrane. Their small size and hydrophobic nature allow them to pass through the lipid bilayer without needing transport proteins or energy input. This is called passive transport.

Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration, driven by the concentration gradient. This movement continues until equilibrium is reached, meaning the concentration becomes uniform. Diffusion does not require energy input from the cell.

Osmosis is a type of diffusion where water moves across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. This movement is crucial for maintaining cell hydration and balancing solute concentrations.

In osmosis, water moves towards the side of the membrane with higher solute concentration to equalize the concentration. If the solute concentration is higher outside the cell (hypertonic), the cell loses water and shrinks. If the solute concentration is lower outside the cell (hypotonic), the cell absorbs water and can swell.

A hypertonic solution has a higher solute concentration than the cell, causing water to leave the cell and potentially lead to shrinkage. A hypotonic solution has a lower solute concentration than the cell, leading to water entering the cell, which can cause it to swell or burst.

Active transport is the movement of molecules across a membrane against their concentration gradient. It requires energy in the form of ATP. An example is the sodium-potassium pump, which utilizes ATP hydrolysis to move sodium ions (Na⁺) out of the cell and potassium ions (K⁺) into the cell, maintaining vital ion gradients.

Anabolic pathways construct complex molecules from simple ones, requiring energy input. Catabolic pathways break down complex molecules into simpler ones, releasing energy. This energy can be used to power anabolic processes.